c++17: drop experimental::filesystem

Use std::filesystem, and drop support for building with experimental
under c++14.

Tested: Build the repo.
Change-Id: I4af0d9c034dbfef5a65153ba5447b86c961aebf1
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>
diff --git a/phosphor-ldap-mapper/Makefile.am b/phosphor-ldap-mapper/Makefile.am
index 1c631e7..7bd58d5 100644
--- a/phosphor-ldap-mapper/Makefile.am
+++ b/phosphor-ldap-mapper/Makefile.am
@@ -12,8 +12,7 @@
 
 phosphor_ldap_mapper_LDFLAGS = $(SDBUSPLUS_LIBS) \
                                $(PHOSPHOR_DBUS_INTERFACES_LIBS) \
-                               $(PHOSPHOR_LOGGING_LIBS) \
-                               -lstdc++fs
+                               $(PHOSPHOR_LOGGING_LIBS)
 
 phosphor_ldap_mapper_CXXFLAGS = $(SYSTEMD_CFLAGS) \
                                 $(PHOSPHOR_DBUS_INTERFACES_CFLAGS) \